Tuesday, 4 June 2002
Investigation of a Visible Reflectance Parameterization for Determining Cloud Properties in Multi-layered Clouds
The current cloud property satellite retrieval technique used for ARM and the Clouds and the
Earth’s Radiant Energy System (CERES) uses parameterizations of reflectance and effective
emittance of cloud layers to simplify the radiative transfer calculations required in determining
the optical depth and effective particle size of clouds from space. These retrievals typically
assume that the cloud in a given pixel is a single-layered plane-parallel cloud. Because
overlapped clouds are common, this assumption often results in cloud properties that represent
some mixture of the multilayered cloud properties and do not provide an accurate assessment of
actual cloud properties in the scene. Various methods using combinations of infrared and solar
channels and solar and microwave data are being used to detect multi-layered clouds. Once
detected, it is necessary to unscramble the properties for each of the cloud layers. If it is assumed
that the properties of the lower layer cloud are known, it should be possible to derive the
properties of the upper-level cloud. This paper investigates the application of the
parameterizations used for the CERES and ARM analyses to obtain the upper-level cloud optical
depth in multilevel cloud situations. Detailed radiative transfer calculations are used to test the
sensitivity and capability of using the visible reflectance parameterization to derive the optical
depth of the upper level cloud given the optical depth and particle size of the underlying cloud
and the surface albedo. This study will provide guidance as to the use of the visible channel
rather than multispectral IR channels to determine the optical depth of the upper cloud layer.
The investigation also examines the error introduced in particle size retrieval when the upper
level cloud is neglected. Methods for determining the lower-layer cloud proeprties are also
discussed.
Supplementary URL: